The Sewer

There is a page to collect right as soon as you land in the sewer. Once you grab it, jump towards the left wall. You will start to climb your way out. Follow the path of jutting stones, they have a slight silver lining.

Climb up to a drainage tube, and use R1 to kick out the grate. Once back outside, go towards the right, and hug the wall to walk along the edge. Once at the end of the wall, jump to the other wall.

Again, climb up to the top. Once up top, there is a green orb chest and two red orb chests tucked back into a jail cell.

Prisoner's Oath Stone can be found in the jail cell with enemies in it. After clearing them out, go in to find the artifact.

After collecting all the orbs, interact with the lever all the way to the left of the stage. This will unleash a few enemies and open up access to a big chain.

Kill the guys, then interact with the chain to open the gate next to it. Go down the hallway that you just opened. This will set up you getting grabbed by some giant hands. Kill off the enemies that get sent your way. When a green shining spot shows up, press R1 to use it as a swing to get out of that building chunk.